Merge branch 'sev/xolonium4-badges' into 'master'

Render badges with Xolonium 4.0

I have recently finished Xolonium 4.0, available [here](https://fontlibrary.org/en/font/xolonium).
Most notably, it now also includes a hinted ttf version. As a result, it should be possible to render the badges with sharper text.

Now, there is no point in just telling you this, so I pushed this branch as a potential update for the badge scripts. It adds the necessary hinting options and slightly adjusts some of the font sizes and positions, to optimize the result. Of course, it is necessary to install the new ttf version first.

Old/New:
![badges-x4](/uploads/d7334628b9d396332c41bb832f409c8e/badges-x4.png)

I also have noticed that the rendered badge images are quite heavy. It would be fairly easy to cut their size by reducing the colors to 8bit, without a noticable effect on quality. I have added an exemplary script (optimize.sh), which could reduce file sizes by almost half.

See merge request !3

diff --cc xonstat/batch/badges/gen_badges.py
Simple merge